"The militants used AK-47, rocket-propelled grenades and other sophisticated firearms," the spokesperson added.

"The injured soldiers were rushed to a local hospital, but three of them succumbed to their injuries later," Newton said.

Assam Director General of Police Mukesh Sahay told IANS: "Our men are on the spot. I will go there from Dibrugarh. We can't say anything about the attack at present. The investigation is on."

Tinsukia Superintendent of Police Mugdhajyoti Mahanta said the National Socialist Council of Nagaland-Khaplang (NSCN-K) and an anti-talk faction of the United Liberation Front of Asom (ULFA) were behind the attack.

On Wednesday, suspected militants had indulged in firing at Pengeri, killing one person and injuring two others.